Previously, many types of devices have been developed in endeavoring to provide an effective means for controlling the amount of evaporation of a liquid on a stove or other heating apparatus. In most cases the liquid is housed in a given volume container and a spring is used that is non adjustable or the adjustment must be made by experimentation. Others use pressure switches which are responsive to a predetermined weight of the container or boils the liquid into another container reducing the weight and opening an electric circuit to turn off the heat source.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following U.S. patents are considered related:
Patent Number Inventor Issue Date 4,334,955 Zoeke et al. Jun. 15, 1982 4,164,644 Remsnyder et al. Aug. 13, 1979 2,070,491 Park Feb. 9, 1937 2,020,364 Lehmann Nov. 12, 1935 Foreign Patents FR2467-577 Santini Oct. 23, 1979 (France)
Zoeke et al. in U.S. pat. No. 4,334,955 teaches a device for controlling evaporation of liquid using a container on a base plate supported by a leaf spring. The spring loaded plate allows the plate to move between two micro switches depending upon the amount of liquid in the container. The switches are connected to a control circuit for activating the heating element and interrupt the flow of power to the heating element when little or no liquid is present in the container.
U.S. Pat. No. 4,164,644 issued to Remsnyder et al is for a heating unit which heats the contents of a container. An electrical circuit is responsive to a pressure switch that reacts to a predetermined weight of material in the container. A pivotally mounted heating element activates a switch which interrupts the circuit in the event of overheating. The heating unit is provided with a heating element having a conical center portion surrounded by an annular flat or planar surface for receiving a container having only a predetermined shaped bottom for accommodating the particular shape heating element.
Park in U.S. pat. No. 2,070,491 discloses a heating system that passes a circuit of high amperage and low voltage power directly thorough a pan. The pan has downwardly projecting prong like contacts which firmly engage the pan to an electric power supply. The high amperage and low voltage may utilize the secondary circuit of a transformer from 110 volt lighting mains. When the heating is completed, a switch energizes a solenoid and power flows thorough to a motor magnet providing the released of the clamps.
Lehmann in U.S. pat. No. 2,020,364 teaches means for adjusting a device for receptacles or containers differing in weight to provide a varying minimum in weight of content to render the heating device ineffective. A tension spring reacts on a lever to separate electrical contacts when the weight of the container and its contents reach a predetermined minimum. The combined minimum weight can be experimentally determined by the adjustment of the spring element when the liquid in the container is just, or slightly more that sufficient to protect the container from overheating. No attention is required to protect the device from overheating since it will automatically shut off when the minimum amount of liquid in the container is reached.
Santini in French patent FR2467-577 discloses a milk bottling appliance using two vessels one taller than the other with a spout on the taller of the two overhanging the smaller vessel. The taller vessel is placed on a heating plate which has a vertical rod passing therethrough which acts as a counterweight holding the plate horizontal against a stop on the rod. When the vessel is filled the weight of the fluid overcomes the counter weight and the lever falls closing a spring contact which closes an electric circuit to the heating element. Once the liquid has boiled over into the smaller vessel the reduced weigh to the heating vessel allows the lever to rise and the spring contacts to opens the electric circuit.